1. Field of the Invention
The present invention relates to a crash attenuator or impact attenuating device to be connected to a vehicle with frame side members as well as a method of transporting such a device.
2. Description of the Related Art
Impact attenuating devices of this type are often referred to as TMAs (Truck Mounted Attenuators) or LMCCs (Lorry Mounted Crash Cushions). The device is mounted on a vehicle, usually a lorry, which is then parked along a roadwork area to protect road-users, men at work and equipment. An impact attenuator can also be used in moving roadworks, such as washing of reflecting posts and painting of road markings. The working vehicle moves slowly and sometimes stands still, which may result in unobservant road-users not having time to make way but colliding with the vehicle. The impact attenuator catches the vehicle and attenuates the collision forces by being deformed, for instance by means of metal constructions with deformation zones or elastic constructions of a polymer material.
Impact attenuating devices of this type are known from, inter alia, EP 0 507 496 A1 and U.S. Pat. No. 5,823,584 A. The EP publication discloses a device which is attached to the frame side members of a lorry and an attenuating part which consists of a deformable metal construction. The device is a single-service protection and is scrapped after a collision. The device has a rear part of an elastic material which can take up light impacts without damaging the more expensive attenuating part. During transport, the attenuating part and the rear part are raised by turning through 90 degrees to reduce the overhang and make driving easier. The US publication discloses an attenuating part of an elastic material, which allows it to be reused after a collision. The device is connected to a lorry by means of a plate which is mounted on the lorry and a wire from the rear part of the attenuating part to a stay on the lorry.
A problem in prior-art impact attenuating devices, like those described above, is that it is difficult to transport the attenuators between the roadwork areas. The attenuators are connected to the rear of the vehicle, which makes the distance between the rear axle of the vehicle and the rearmost point of the attenuator, the overhang, long, in most cases several meters. A long overhang causes great problems in sharp bends, intersections, roundabouts etc. As the vehicle turns, the overhang sweeps over a large area outside the vehicle's own lane, and in some traffic environments, it will be difficult to transport the device.
A further problem is that great modifications of the vehicle are necessary for carrying prior-art attenuators. These modifications are not only expensive but also cause an inflexible system where only certain vehicles which have been modified in advance can use attenuators. Using today's system in which contractors are employed to a large extent, it is a great advantage to be able to call in any vehicle whatever and connect an attenuator.
One more problem of prior-art attenuators is that the rear end of the attenuator moves up and down in relation to the roadway depending on the wheels and spring system of the vehicle. When the vehicle runs down into a hole in the road there is a risk that the rear end of the attenuator scrapes against the ground, and when the vehicle passes a hill-top there is a risk that the attenuator is raised to such an extent that a colliding vehicle may be wedged under the attenuator.